Hidden Desire (1998)

Bill Manning is a private detective down on his luck. So he takes on a dirty job for a wealthy man who's anxious to get out of his marriage. Trailing the rich man's wife, Manning ends up falling for the very woman he's been hired to destroy. He goes through with his end of the deal, but then has to figure out a way to undo the damage he's done and win the heart of the woman he was hired to betray.